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Knitting navel lint

Could one knit a sweater from human navel lint? — Craig Charles, Dallas

Good thinking, Craig. Why waste this valuable resource? And why stop at lint? Think of the environmentally sensitive duds one might make from used dental floss, or the hair fished from bathtub drains.

Still, one does wonder whether lint has what it takes to be a practical textile feedstock. Luckily the navel-lint research community has come through. Of particular note is Georg Steinhauser of the Vienna University of Technology, who in 2009 published "The Nature of Navel Fluff" in the journal Medical Hypotheses.

Georg ascertained a number of important facts about navel lint, which we'll review shortly. And what did he get for his trouble? Abuse, that's what. No sooner had his article hit the streets than the Annals of Improbable Research, which specializes in calling attention to what it considers risible scientific inquiry, published a "special Navel Lint issue."

Back to Georg's article:

• He collected an astonishing 503 lint samples over three years and individually weighed them, displaying his results in a mass distribution chart. We learn that the average sample weight was 1.82 milligrams—that is, 1.82 thousandths of a gram.

• Navel lint, or at any rate Georg's, consists of cotton cellulose fibers mixed with skin cells, fat, and sweat.

• Men produce the most. Georg hypothesizes this is because abundant male abdominal hair surrounding the belly button scrapes the lint free from the subject's cotton clothing and channels it into the navel. When he shaved the area around his belly button, lint production plunged.

• The total weight of Georg's collected lint—three years' worth, mind you—was less than a gram.

My assistant Una calculated that getting enough for a long-sleeve cotton top, which for some reason she thought was a better benchmark than a sweater, would take 150 years; a cotton sweatshirt would take about 752 years. However, could we even do it?

Sadly, the answer is almost certainly no. Most spinning processes need an average fiber length of at least two-thirds of an inch, much longer than you'd expect to find in navel lint. Remember the reason navel lint is there in the first place is that it worked loose from whatever you were wearing.

We humans like stroking because grooming is a social activity among primates. But if we stroke other animals that can't stroke back due to a lack of hands, they still seem to feel pleasure. Shed some light? — Thorsten

I don't know about all animals. I've never noticed that stroking snails sends them into ecstasies. But most mammals seem partial to it, no doubt in the big-picture sense because, as you say, it promotes grooming and bonding. In fact, there's reason to think stroking is so important that we higher-order vertebrates now like it because that's the way we're wired, with certain neurons in the skin that respond only to stroking.

How do we know this? Because of the following bizarre experiments:

• Human subjects were stroked on forearms and palms by robots at various speeds and asked to report which strokes felt the nicest. Meanwhile, researchers monitored what they figured were the stroke receptor neurons via electrodes they'd hooked up. Findings: (1) volunteers most liked being stroked between a half inch and four inches per second, and (2) neurons believed to be stroke receptors fired fastest within that range.

• Mice were bred so that fluorescent molecular markers attached to their stroke receptor neurons lit up when activated. Then researchers sliced open each mouse's spinal column so they could view the far end of the stroke receptor neurons with a microscope sensitive to extremely low light. Sure enough, when the mice were stroked, the stroke receptor neurons emitted tiny flashes.

Conclusion: the pleasure we take in a caress is basically an electrical response. cs